Does hearing loss cause cognitive impairment and dementia? And can you prevent or delay cognitive loss with hearing aids? These are tough questions to answer.
Multiple studies have tackled the issue. One meta-analysis from February analyzed 11 studies dating back to 2016 to find that older people with moderate to severe hearing impairment had a 29 to 57 percent greater risk of cognitive impairment than those with normal hearing. It did not find that wearing hearing aids reduced the risk.
A 2016 study analyzing health insurance claims of 154,783 seniors concluded that hearing impairment increases the risk of dementia and that to some extent this happens regardless of medical treatment. Though the authors said hearing aids might delay or prevent dementia, they didn’t have details on whether patients were prescribed hearing aids or were using them regularly.
However, a 2017 article in Frontiers in Aging Neuroscience cited two studies that found people wearing hearing aids improved their performance on cognitive tests. The article said hearing aids, when prescribed at the beginning of age-related hearing loss, can postpone cognitive side effects.
Dementia causes damage before symptoms emerge
There aren’t definitive answers because the field is still new, according to Dr. Jennifer Deal of the Cochlear Center for Hearing and Public Health at Johns Hopkins University. She noted that studies of dementia have traditionally focused on pathology or vascular disease and that Dr. Frank Lin, the director of the Cochlear Center, has been doing much of the work of bringing hearing into the discussion.
By the time someone shows symptoms of dementia, “the damage has already been done to the brain. We can’t actually reverse that, so the idea is we want to try to prevent it from happening in the first place.” As the population ages, this will increasingly be a public health concern, she said.
Deal said hearing is one of the only later-life risk factors that could potentially delay cognitive decline. A 2017 article by the Lancet Commission on Dementia Prevention, Intervention and Care estimated up to 35 percent of dementia could be prevented due to modifiable risk factors, and the biggest of those is hearing loss, at 9 percent. The potential proportion of dementia that could be prevented if hearing loss was prevented or treated is about 90 percent. “And the reason why it’s so high is that so many people have it,” Deal said, adding that two-thirds of people over age 70 have clinically meaningful hearing loss.
Hearing loss impacts much of the brain
Why is hearing loss associated with dementia? Deal said one possibility is that something else, such as vascular disease, causes both conditions.
Another is the strain on people with hearing loss in trying to interpret sounds. That can impact memory, Deal said. “We call that effortful listening, and that’s why people with hearing loss say it sounds like you’re mumbling.”
MRI studies have shown that people with hearing loss use parts of the brain beyond the auditory cortex to decode sounds, so hearing loss affects much of the brain. Deal said Lin has published a study showing a faster decline in brain volume in people with hearing loss than in people with normal hearing.
Social isolation is also likely a factor because it’s associated with health issues, Deal said. “If we have difficulty with hearing in noisy environments, maybe we don’t go out to dinner as often, or attend church functions or other kinds of social engagements, and in that way can become more isolated.”
But these are hypotheses, and researchers don’t know whether medical care has an impact. There are many factors in who uses a hearing aid, including its affordability, Deal said. “It’s hard for us to make a full judgment in terms of whether or not there’s actually a difference being made by the hearing aid, or whether we’re just comparing two groups we really shouldn’t be comparing.”
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The Cochlear Center is trying to get answers. They’re recruiting 850 people around the country, older adults with mild to moderate hearing loss and normal cognitive skills who don’t use hearing aids. Some participants will receive hearing aids and some won’t, and the researchers will track their cognitive levels. Deal said they’ll have the results in 2022. “This is the type of study, with the randomization component, that really should help give us a definitive answer about whether or not hearing aid treatment can help delay cognitive decline.”
What should people do in the meantime? “If you have any concerns about your hearing or any other kind of health issues, I always encourage people to talk to their doctors,” Deal said. It may not be clear whether hearing aid use impacts cognition, “but we do know that hearing loss can be impactful in other ways.”